in-group 
noun
An exclusive, typically small, group of people with a shared interest or identity: an in-group signal of ethnic identity special forms of speech are used in some kinds of in-group...
- This heightened awareness becomes personally relevant when one commits to identifying with the ethnic in-group.
- I think there's another side to it as well, seen from the other side of the fence: incoming slang is a sort of secret language, expressing exquisitely shaded meanings that are shared among the in-group but are baffling to outsiders.
- Such dialects, almost by definition, are media of intimacy: ‘mother tongues’ used in the family and in-groups.